1. Technical Field
The present invention relates to a method of manufacturing an inertial sensor.
2. Description of the Related Art
Recently, an inertial sensor has been used as various fields, for example, the military such as an artificial satellite, a missile, an unmanned aircraft, or the like, vehicles such as an air bag, electronic stability control (ESC), a black box for a vehicle, or the like, hand shaking prevention of a camcorder, motion sensing of a mobile phone or a game machine, navigation, or the like.
The inertial sensor generally adopts a configuration in which a flexible substrate such as membrane is bonded to a mass body so as to measure acceleration and angular velocity Through the configuration, the inertial sensor may calculate the acceleration by measuring inertial force applied to the mass body and may calculate the angular velocity by measuring Coriolis force applied to the mass body.
In detail, a process of measuring the acceleration and the angular velocity by using the inertial sensor is as follows. First, the acceleration may be implemented by Newton's law of motion “F=ma”, where “F” represents inertial force applied to the mass body, “m” represents a mass of the mass body, and “a” is acceleration to be measured. Therefore, the acceleration a may be obtained by measuring a force F applied to the mass body and dividing the measured force by the mass m of the mass body that is a predetermined value. Meanwhile, the angular velocity may be obtained by Coriolis force “F=2mΩ·v”, where “F” represents the Coriolis force applied to the mass body, “m” represents the mass of the mass body, “Ω” represents the angular velocity to be measured, and “v” represents motion velocity. Among others, since the motion velocity V of the mass body and the mass m of the mass body are recognized in advance, the angular velocity Ω may be obtained by measuring the Coriolis force (F) applied to the mass body.
As described above, when the inertial sensor measures the acceleration a by using the inertial force F, the mass body is displaced by the inertial force F and when the inertial sensor measures the angular velocity Ω by using the Coriolis force F, the mass body is vibrated by a predetermined motion velocity V. As described above, in order to measure the acceleration a or the angular velocity Ω, the movement of the mass body is essential and thus, a cap protecting the inertial sensor is provided with a cavity so as to secure a space in which the mass body may move.
With reference to the process of forming the cavity in the cap, FIGS. 1 to 6 show process cross-sectional views showing a method of manufacturing an inertial sensor according to the prior art. The problems of the prior art will be described with reference to FIGS. 1 to 6.
First, as shown in FIG. 1, a process of applying a photosensitive resist 2 to a substrate 1 is performed. In this case, the photosensitive resist 2 is to optionally perform wet etching on the substrate 1. As the photosensitive resist 2, a dry film or a liquid-phase photosensitive material may be used.
Next, as shown in FIG. 2, a process of optionally hardening the photosensitive resist 2 is performed. In detail, a photomask 3 adheres to the photosensitive resist 2 and is then exposed to ultraviolet rays (an arrow) to harden a border of the photosensitive resist 2.
Next, as shown in FIG. 3, a process of patterning the photosensitive resist 2 is performed. In this case, a central portion of the photosensitive resist 2, which is not hardened, is dissolved by a developer such as sodium carbonate, potassium carbonate, or the like, and then removed.
Next, as shown in FIG. 4, a process of forming the cavity 4 on the substrate 1 is performed. The photosensitive resistive 2 remains only on a portion corresponding to the border of the substrate 1 since the photosensitive resist 2 is patterned at the previous step. Therefore, when the substrate 1 is subjected to the wet etching by using the photosensitive resist 2 as an etching resist, the cavity 4 may be formed at the central portion of the substrate 1.
Next, as shown in FIG. 5, a process of removing the photosensitive resist 2 from the substrate 1 is performed. The photosensitive resist 2 is not needed any more since the cavity 4 is formed on the substrate 1 at the previous step and the manufacture of a cap 5 may complete by removing the photosensitive resist 2 at the present process.
Next, as shown in FIG. 6, a process of bonding the cap 5 on a device substrate 6 is performed. In this case, the device substrate 6 substantially serves to measure the acceleration or the angular velocity and the cap 5 is bonded to the device substrate 6 after applying an adhesive 7 to the border of the cap 5.
As described above, in the method of manufacturing an inertial sensor according to the prior art, the photosensitive resist 2 that has fulfilled its part is removed after the cavity 4 is formed on the substrate 1. As a result, there is a problem in that the photosensitive resist 2 may not be used any more (see FIGS. 4 and 5). In addition, when the adhesive 7 is applied to the border of the cap 5, it is difficult to form the adhesive 7 and the thickness of the adhesive 7 is not constantly formed due to a step occurring by the cavity 4 (see FIG. 6). Therefore, the adhesion between the cap 5 and the device substrate 6 is weak, thereby degrading structural stability of the inertial sensor.